The present invention relates to an apparatus for continuously measuring the flow volume of a fluid medium especially air, which passes through a variable cross-section throttling point, such as the air throttle of a carburetor for an internal combustion engine.
Methods are known, such as described in German Pat. No. 2,311,484, dated Oct. 3, 1974, for testing the volume flow of a fluid medium at a variable cross-section throttle point, including the air supply metering device for electronic fuel injection engines arranged in series. The throttle to be tested is between two constant cross-section test nozzles. One of the nozzles is located upstream of the throttle, and provides a constant flow volume of air. The second nozzle, located downstream of the throttle to be tested, maintains constant pressure of the medium at the outlet of the throttle, and is not in any way related to the measurement of the flow volume. Such constant outlet pressure may alternatively be provided by use of a vacuum pump arranged downstream of the throttle.
According to the known methods, the fluid pressure at a point between the first nozzle and the test throttle is measured and compared to a calibration fluid pressure value associated with a sample throttle. From this comparison it is determined whether the measured fluid pressure corresponds to the required fluid pressure value associated with that fluid volume for the sample throttle.
Difficulties occur in the known method of testing the fluid flow volume at a throttling point, as described above, when the throttling point has a variable cross-section, such as the air throttle of a carburetor. In that case, every different throttle setting has a different cross-section area through which the fluid medium must pass. As a result of the change in the throttle, it is necessary to change the cross-section of the first nozzle to correspond to different throttle settings. This has been accomplished by providing either a plurality of nozzles upstream of the throttle point to be tested or by providing nozzles having calibrated variable cross-sections.
It is therefore an object of the present invention to provide a new and improved apparatus for testing the fluid flow volume passing through a variable cross-section throttle accurately and without the need for repetitious calculations or for equipment having multiple configurations.